1. Field of the Invention
The present invention relates to a converter motor, which is an AC motor assembly comprising a multi-phase AC motor of induction type operated by a static converter.
2. The Prior Art
Since static converters in modern times have displayed a rapid development particularly after the introduction of controlled semiconductor rectifiers, thyristors, for high powers, there has been an increasing interest in converter operation of motors of various kinds and sizes. This applies above all to asynchronous motors, which offer an extremely simplified alternative to AC motors and synchronous motors. Many different systems are already known for operation of asynchronous motors at various speeds. It is, however, a problem to achieve stable and simultaneously optimum operating conditions at varying speeds as may occur, for example, in the case of traction and crane operation.
It is desirable in this connection to be able to increase or reduce the speed rapidly while maintaining a maximum torque, which may be fixed at a given limit, and in this way make sure that the change of frequency never becomes so great that the resulting slip results in an unstable torque curve. The problems here are, among other things, constantly to measure and control the torque and the slip, which is inconvenient when it is a question of controlling and regulating purposes and the conditions are not stationary.